1. Field of the Invention
The invention relates to a method for burning lumpy stock, in particular limestone, dolomite brick, magnesate brick or other carbonate rock, in at least one shaft which comprises a preheating zone, a burning zone and a cooling zone, wherein coal is supplied via burner lances.
2. Description of the Related Art
The fuel costs for lime burning are considerable and may account for more than 50% of the production costs. Since coal is in most cases the cheapest energy source, most lime kilns are nowadays coal-fired. Coal can however vary greatly in terms of its properties. For example, a high content of ash and sulfur has an adverse effect, as the burnt lime is undesirably contaminated.
A particular characteristic of coal is its swelling index. From numerous practical tests, it is known that it has hitherto not been possible for coal with a swelling index of greater than 1.0 to be used in lime kilns, in particular in parallel flow-counter flow regenerative lime kilns, as severe operational problems were encountered, such as for example blockage of the burner lances and burn-up of the burner lances owing to oxidation or melting. Owing to the restricted usability of such coals in PCR shaft-type lime kilns, it has hitherto been the case that either a cylindrical rotary kiln has been used, or petroleum coke or liquid or gaseous fuels have had to be used. Cylindrical rotary kilns however have the considerable disadvantage that they consume 50-100% more fuel than PCR lime kilns, and consequently also discharge a much greater amount of CO2 into the atmosphere. The use of petroleum coke is also disadvantageous, as its sulfur content can be up to 10 times that of coal, giving rise to further limitations. Furthermore, liquid and gaseous fuels are under some circumstances not available, or are much more expensive than coal.
DE 32 27 395 C2 discloses a method for producing briquettes for the fixed bed of a gasifier reactor or shaft-type kiln, wherein 30-85% non-caking raw coal and 15-70% caking raw coal are mixed and subsequently formed into briquettes, wherein the caking coal has a caking capacity (swelling index) of ≥5.